Electric lamp and discharge devices: systems – Cathode ray tube circuits – Combined cathode ray tube and circuit element structure
Reexamination Certificate
1998-06-10
2001-08-21
Bettendorf, Justin P. (Department: 2817)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Combined cathode ray tube and circuit element structure
C315S505000, C313S359100
Reexamination Certificate
active
06278239
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to linear accelerators, electrical switches and more particularly to very high-voltage and high-current switches, such as are needed for dielectric-wall linear accelerators and pulse-forming lines that operate at high gradients, e.g., in excess of twenty megavolts per meter.
2. Description of Related Art
Donald W. Hunter describes a laser-initiated dielectric-breakdown switch in U.S. Pat. No. 5,249,095, issued Sep. 28, 1993. Such switches are used in safe and arm systems for initiating exploding foil initiators. One electrode has an opening which allows light from a laser source to shine on dielectric material to induce voltage breakdown. Electrical conduction is precipitated through a dielectric, by solid dielectric breakdown between the electrodes, and this switch closing allows energy to pass from a power supply to the electronic foil initiator (EFI). Switches with high voltage ratings, e.g., tens of thousands of volts, are needed to hold off the magnitude of voltages typically found on an energy storage capacitor, e.g., 2-3 kilovolts (kV), for a single EFI. When triggered, such switches must produce an unusually fast rise time pulse, in order to initiate the EFI. Typical pulses must have stored energies of 0.3-0.6 millijoules, rise times of 30-60 nanoseconds, peak currents of 3-7 kiloamps (kA), and peak powers of 5-15 megawatts (MW). A commonly used switch for such applications is the ceramic body, hard brazed, miniature spark gap, with either an internal vacuum or a gas filled volume. But such spark gaps require hermetic sealing, are expensive, have marginal reliability and operating life, and require an expensive high voltage trigger circuit. One other switch in use for this application is the explosively initiated shock conduction switch which uses a primary explosive detonator. But this presents handling problems and can produce chemical contamination and possible explosive damage to surrounding electronics.
Other, conventional types of miniature switches include embedded electrode dielectric breakdown switches, e.g., as marketed by Mound Labs MLM-MC-88-28-000, reverse-bias diode avalanche switches, e.g., as marketed by Quantic Industries and Mound Labs, that are either electrically or light initiated, and gallium arsenide bulk conduction switches. But embedded electrode dielectric breakdown switches require a high voltage and a relatively high-energy trigger pulse from an expensive trigger circuit. Reverse bias diode avalanche switches require a significant number of components for both the switch and trigger circuit. Gallium arsenide switches are expensive, may require hermetic sealing, and often require high power for initiation, e.g., much more power than a laser diode can provide.
Particle accelerators are used to increase the energy of electrically-charged atomic particles, e.g., electrons, protons, or charged atomic nuclei, so that they can be studied by nuclear and particle physicists. High energy electrically-charged atomic particles are accelerated to collide with target atoms, and the resulting products are observed with a detector. At very high energies the charged particles can break up the nuclei of the target atoms and interact with other particles. Transformations are produced that help to discern the nature and behavior of fundamental units of matter. Particle accelerators are also important tools in the effort to develop nuclear fusion devices.
The energy of a charged particle is measured in electron volts, where one electron volt is the energy gained by an electron when it passes between electrodes having a potential difference of one volt. A charged particle can be accelerated by an electric field toward a charge opposite that of the charged particle. Beams of particles can be magnetically focused, and superconducting magnets can be used to advantage. Early machines in nuclear physics used static, or direct, electric fields. Most modern machines, particularly those for the highest particle energies, use alternating fields, where particles are exposed to the field only when the field is in the accelerating direction. When the field is reversed in the decelerating direction, the particles are shielded from the field by various electrode configurations.
The simplest radio frequency accelerator is the linear accelerator, or linac, and comes in different forms, depending electrons or ions are to be accelerated. For accelerating ions, frequencies of under 200 MHz are used. The ions are injected along the axis of a long tank excited by high-power radio frequency in an electric field along the axis. The ions are shielded from the decelerating phases by drift tubes in the tank through which the beam passes. As the particles gain energy and velocity, they travel farther. Therefore, the drift tubes must be longer toward the end of the tank to match the period of the accelerating field.
The first linear accelerator had three drift tubes and was built in 1928 by Rolf Wideroe of Norway. Sodium and potassium ions were accelerated to demonstrate the principle of radio frequency acceleration. During the 1930's, the University of California did further work on ion-type linear accelerators. But application of the principle was delayed until after World War II because of a lack of high-power radio frequency amplifiers. The development of radar provided such amplifiers. Shortly after the war, Luis Walter Alvarez built the first proton linear accelerator in which protons reached an energy of 32 million electron volts (MeV). Two megawatts were required at a frequency of about 200 MHz and limited the machine to one millisecond pulses.
Since 1950, several proton and ion linear accelerators have been built, some as injectors for still larger machines and some for use in nuclear physics. A large modern accelerator is the 800-MeV machine at the Los Alamos Scientific Laboratory, New Mexico, and is used as a meson factory in the study of intermediate-mass particles, e.g., those with masses heavier than the electron and lighter than the proton. These intermediate-mass particles seem to provide the force that binds atomic nucleus.
Because electrons are much lighter than ions, their velocity at a given energy is significantly higher than that of ions. The velocity of a one-MeV proton is less than five percent that of light. In contrast, a one-MeV electron has reached ninety-four percent of the velocity of light. This makes it possible to operate electron linacs at much higher frequencies, e.g., about 3,000 MHz. The accelerating system for electrons can be a few centimeters in diameter. The accelerating systems for ions need diameters of a few meters. Electron linacs having energies of ten to fifty MeV are widely used as x-ray sources for treating tumors with intense radiation.
A very large electron linac, which began operation in 1966 at the Stanford Linear Accelerator Center (California), is more than 3.2 km (2 mi.) long and has been able to provide electrons with energies of fifty billion electron volts (50 GeV). The Stanford Linear Collider can provide relative collisions that produce energies of more than 100 GeV between a beam of electrons and a beam of positrons that are aimed to collide head-on.
Such conventional accelerators are primarily useful for low currents, due to the interaction of the beam with the accelerator structure and the applied electric field. Induction accelerator types avoid many such problems.
FIG. 1
shows a cross-section of a single induction accelerator cell in which an accelerating voltage appears only across an internal accelerating gap. The cell housing and the outside of the accelerator are at ground potential. A large number of induction cells can be stacked in series to produce high energy beams without needing proportionately high voltages outside the accelerator that can be dangerous and troublesome to maintain. The core is a solid cylinder of either ferro-magnetic or ferri-magnetic with a coaxial central hole for the beam current. The core imparts a very
Caporaso George J.
Kirbie Hugh C.
Sampayan Stephen E.
Bettendorf Justin P.
Caress Virginia B.
Daubenspeck William C.
Main Richard B.
The United States of America as represented by the United States
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